Old English under (prep.) "beneath, among, before, in the presence of, in subjection to, under the rule of, by means of," also, as an adverb, "beneath, below, underneath," expressing position with reference to that which is above, from Proto-Germanic *under- (cognates: Old Frisian under, Dutch onder, Old High German untar, German unter, Old Norse undir, Gothic undar), from PIE *ndher- "under" (cognates: Sanskrit adhah "below;" Avestan athara- "lower;" Latin infernus "lower," infra "below").

Productive as a prefix in Old English, as in German and Scandinavian (often forming words modeled on Latin ones in sub-). Notion of "inferior in rank, position, etc." was present in Old English. With reference to standards, "less than in age, price, value," etc., late 14c. As an adjective, "lower in position; lower in rank or degree" from 13c. Also used in Old English as a preposition meaning "between, among," as still in under these circumstances, etc. (though this may be an entirely separate root; see understand).

Under the weather "indisposed" is from 1810. Under the table is from 1921 in the sense of "very drunk," 1940s in sense of "illegal." To get something under (one's) belt is from 1954; to keep something under (one's) hat "secret" is from 1885; to have something under (one's) nose "in plain sight" is from 1540s; to speak under (one's) breath "in a low voice" is attested from 1832. To be under (someone's) thumb "entirely controlled" (by that person) is recorded from 1754.

1816, "underhand" (in reference to a style of throwing), from under + arm (n.1). First attested 1908 in dressmaking sense of "seams on the lower half of the arm-hole;" as a euphemism for armpit, it is attested from 1930s, popularized by advertisers.

c.1600, from under + belly (n.). In figurative sense of "most vulnerable part" it is recorded from Churchill's 1942 speech. Sometimes used erroneously or euphemistically in sense of "seamy or sordid part" of anything.

1660s, "stream of water or air flowing beneath the surface or beneath another current," a hybrid formed from under + current (n.). The figurative sense of "suppressed or underlying character" is attested from 1817.

late 14c., "to cut down or off," from under + cut (v.). In the commercial sense of "sell at lower prices" (or work at lower wages) it is first attested 1884. Figurative sense of "render unstable, undermine" is recorded from 1955, from earlier literal meaning "cut so as to leave the upper portion larger than the lower" (1874).

c.1200, underfot "under the feet," from under + foot (n.). Compare similarly formed Middle Dutch ondervoete. As an adjective, attested from 1590s; in reference to persons, "continually in the way," it is recorded from 1891. Middle English under fot meant "vanquished, overcome."

1570s, "below the surface," from under + ground (n.). As an adjective, attested from c.1600; figurative sense of "hidden, secret" is attested from 1630s; adjectival meaning "subculture" is from 1953, from adjectival use in reference to World War II resistance movements against German occupation, on analogy of the dominant culture and the Nazis. Noun sense of "underground railway" is from 1887 (shortened from phrase underground railway, itself attested from 1834).

"network of U.S. anti-slavery activists helping runaways elude capture," attested from 1847, but said to date from 1831 and to have been coined in jest by bewildered trackers after their slaves vanished without a trace. Originally mostly the term for escape networks in the (then) western states of the U.S.

mid-14c., "by secret means, stealthily, in a surreptitious manner," from under + hand (n.). Perhaps the notion is of the hand turned over (thus concealing what it holds). Compare Middle Dutch onderhanden "by degrees, slowly," Dutch onderhandsch "secret, private." The adjective is attested from 1540s. Old English under hand meant "in subjection, in (one's) control or power."

in reference to a throw, etc., "performed or done with the knuckles turned under," 1807, from under + hand (n.). Compare underhand. As "in secret," from 1825; as "with too few people," from 1834. Related: Underhandedly; underhandedness.

Old English under lecgan "to support by placing something beneath;" see under + lay (v.). Related: Underlaid; underlaying. Compare similarly formed Old High German Related: untarleccan, German unterlegen.

Old English under licgan "to be subordinate to, to submit to;" see under + lie (v.2). Meaning "to lie under or beneath" is attested from c.1600; figurative sense of "to be the basis of" is attested from 1852 (implied in underlying). Similar formation in Old High German untarliggan; German unterliegen.

c.1300, undermyne, "render unstable by digging at the foundation," from under + mine (v.). The figurative sense "injure by invisible, secret, or dishonorable means" is attested from early 15c. Similar formation in Dutch ondermijnen, Danish underminere, German unterminiren. The Old English verb was underdelfan. Related: Undermined; undermining.

an obsolete Old English and Middle English word for "morning;" in Old English originally "third hour of the day; 9 a.m." (corresponding to tierce). Hence underngeweorc, undernmete "breakfast." Common Germanic: Old Frisian unden, Old Saxon undorn, Middle Dutch onderen, Old High German untarn, Old Norse undorn; of uncertain origin. By extension, "period from 9 a.m. to noon;" but from 13c. shifting to "midday, noon" (as in undern-mete "lunch," 14c.); and by late 15c. to "late afternoon or early evening."